Motor-driven stair lift devices are commonly used to assist the physically handicapped in traversing a staircase. A conventional stair lift comprises a carrier or platform depending from a track mounted on a wall or side of the staircase. The platform is secured to a chain actuated by a motor-driven sprocket to drive the carrier up and down the staircase.
Significant disadvantages are inherent in such a device. Primarily, the inflexibility of a chain renders it difficult to install such a device around corners, such as where the staircase includes a landing. Furthermore, complex and expensive means must be utilized to prevent the carrier from free-falling in the event of a power interruption or breakage of the chain or drive mechanism.
Attempts have been made to overcome the problem of cornering by using a series of flexibly linked elements encased in a track, such as described in U.S. Pat. No. 4,627,517. Such a system is still subject to the danger of free-fall resulting from power outage or breakage or malfunction in the drive mechanism. Replacement of individual transmission elements can be difficult because of the manner in which they are connected. Moreover, as each individual transmission element is not free rolling, unnecessary wear occurs due to frictional resistance of the tubular casing.
The present invention overcomes these disadvantages by providing a stair lift utilizing a series of unconnected free rolling spheres abutting one another in a tubular track. The spheres are driven by a worm, whose axis is oriented parallel to the axis of the track, thus minimizing opportunity for breakage of the drive shaft and in any event providing an automatic safeguard against free-fall. In the event of power interruption or breakage of the motor or drive shaft, the worm stops revolving and acts as an abutment preventing movement of spheres within the track.
The advantages of cornering are easily obtained in such a system, and a broken or damaged sphere can be removed and replaced easily, since adjacent spheres do not interlock or interconnect in any fashion. Much wear and tear on the spheres is reduced because they are free rolling, thus enabling each individual sphere to roll against the direction of greatest friction.